The present invention relates to a fluorescent display device and a method for driving same, wherein the device has anode electrodes having fluorescent layers formed thereon and control electrodes for controlling the electron emission from a filament installed therebetween.
One type of conventional fluorescent display device is provided with anode electrodes, control electrodes and a filament disposed therebetween, wherein each anode electrode has a fluorescent layer formed thereon and the electron emission from the filament is controlled by varying the voltage applied to the control electrodes.
FIGS. 5A and 5B set forth a structure of such a conventional fluorescent display device. FIG. 5A is a plan view depicting the arrangement of anode electrodes, control electrodes and a filament. FIG. 5B sets forth a cross sectional view taken along Z-Zxe2x80x2 of FIG. 5A. In FIGS. 5A and 5B, there are illustrated a back plate 51 of the fluorescent device, control electrodes (back plate electrodes) 551 to 555 formed on the back plate 51, a front plate 52, anode electrodes 561 to 565 formed on the front plate 52, the anode electrodes 561 to 565 respectively having fluorescent layers 571 to 575 coated thereon, and a filament 53 tightly hanged between the anode electrodes 561 to 565 and the control electrodes 551 to 555 by two supporting members 54 and 54xe2x80x2 disposed on the back plate 51.
When a control electrode, e.g., 552, is biased to have a voltage, e.g., 25V, higher than the one applied to the filament 53, electrons emitted from the filament 53 are prevented from arriving at its corresponding anode electrode, e.g., 562. However, a low voltage, e.g., 12V, is applied to a control electrode, electrons from the filament 53 can reach its corresponding anode electrode. For instance, when the control electrodes 552 and 555 are biased at 12V while other control electrodes 551, 553 and 554 are biased at 25V, the electrons emitted from the filament 53 can reach only the anode electrodes 562 and 565 corresponding to the control electrodes biased at the low voltage and therefore, only the fluorescent layers 572 and 575 on the anode electrodes 562 and 565 are allowed to emit light.
However, when a high voltage is applied to a control electrode to prevent electrons emitted from the filament from arriving at a corresponding anode electrode in the conventional fluorescent display device described above, electrons are, instead, emitted from the filament toward the control electrode biased at the high voltage, thereby resulting in a current flowing through he control electrode. For this reason, the prior art fluorescent display device unnecessarily consumes considerable power even when none of the anode electrodes are selected to be turned on to emanate light. Further, since electrons are emitted from the filament even when an anode electrode is not selected to be turned on to emit light, some of the emitted electrons may reach the unselected anode electrode, causing leakage luminescence to occur.
In addition, since the high voltage is required to suppress the electron emission from the filament toward the unselected anode electrode, a high voltage driving circuit becomes necessary.
It is, therefore, a primary object of the present invention to provide a slim fluorescent display device capable of reducing a power consumption, luminescence with a low driving voltage and minimizing a leakage luminescence with a low driving voltage.
In accordance with one aspect of the present invention, there is provided a fluorescent display device having control electrodes and anodes, each anode having an anode electrode and a fluorescent layer formed thereon, and a filament installed between the control electrodes and the anode electrodes,
wherein when an anode is selected to be turned on to emit light, a first voltage is applied to the filament, a second voltage is applied to the selected anode and a third voltage is applied to a control electrode facing the selected anode, the second voltage being higher than the first voltage and the third voltage is not lower than the first voltage; and wherein when a voltage applied to a target control electrode is lower than a voltage applied to the filament by more than a predetermined voltage difference, an anode facing the target control electrode is riot turned on to emit light even when the second voltage is applied thereto.
In accordance with another aspect of the present invention, there is provided a method for driving a fluorescent display device having control electrodes and anodes, each anode having an anode electrode and a fluorescent layer formed thereon, and a filament installed between the control electrodes and the anode electrodes, wherein when an anode is selected to be turned on to emit light, a first voltage is applied to the filament, a second voltage is applied to the selected anode and a third voltage is applied to a control electrode facing the selected anode, the second voltage being higher than the first voltage and the third voltage is not lower than the first voltage; and wherein when a voltage applied to a target control electrode is lower than a voltage applied to the filament by more than a predetermined voltage difference, an anode facing the target control electrode is not turned on to emit light even when the second voltage is applied thereto.